Combination catheter for invasive probe delivery and balloon dilation

ABSTRACT

A catheter for delivering both a probe and a balloon to a lumen in a subject. The probe is most preferably an ultrasonic imaging probe and the balloon a dilation balloon. The catheter comprises, at a proximal end, a triple lumen section that comprises a guidewire lumen, a probe lumen and a lumen for communicating with a balloon. As the lumens run toward the distal end of the catheter, a transition section is provided that merges the probe lumen and the guidewire lumen into a single lumen. The single lumen continues distally and is surrounded by the balloon. Distal of the balloon, the single lumen defines an imaging window section. The catheter terminates in a distal tip that is preferably tapered along both its inner and outer diameters; the tip comprises a distal lumen sized to accept a guidewire. In certain preferred embodiments, radio opaque markers are used to delineate the various sections of the catheter. Among its many advantages, the present invention readily permits back loading of a guidewire.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.773,037 filed on Oct. 8, 1991, now issued as U.S. Pat. No. 5,201,315entitled "Ultrasonic Imaging Sheath" and U.S. patent application Ser.No. 11,335 filed on Jan. 29, 1993 now U.S. Pat. No. 5,249,580, adivision thereof, both naming James M. Griffith as the inventor, theentirety of which are incorporated by reference as if fully set forthherein.

The present invention relates to invasive therapeutic and diagnosticdevices, such as intravascular ultrasound imaging devices and balloondilation catheters. More particularly, improved catheters and methodsfor their use are disclosed that place imaging and dilation functionsinto a single catheter. The present invention therefore allows reducedcost and catheterization time when compared with using separatecatheters for the two functions.

BACKGROUND OF THE INVENTION

Dilation catheters without ultrasound capability are well known andaccepted. For example, angioplasty for coronary and leg arteries iscommon. Various companies market dilation catheters, including: SciMedLife Systems, Minneapolis, Minn.; Advanced Cardiovascular Systems, SantaClara, Calif.; and USCI, Billerica, Mass.

Catheters for ultrasound imaging, especially for imaging coronary arterygeometry, are also well known and are marketed by several companiesincluding: Diasonics, Milpitas, Calif.; Cardiovascular Imaging Systems,Sunnyvale, Calif.; Endosonics, Pleasanton, Calif.

The benefits of a single catheter providing both dilation and ultrasoundimaging, rather than two separate catheters, include decreased cost andcatheterization time. Decreasing catheterization time allows a givencatheterization facility and staff to serve more patients; among otherbenefits, this fact will likely decrease the patient's cost. Also,certain patients find catheterization somewhat frightening anduncomfortable. Presumably, they would prefer a faster procedure.

The potential for a combined dilation/imaging catheter has beenrecognized, for example, in U.S. Pat. No. 4,951,677--Crawley, et. al.,describing a catheter sheath with a dilation balloon mounted over anultrasound transducer so that an area can be imaged while it is openedwith the balloon. This device, however, has certain limitations. It isnot adapted for use with the steerable guidewires that physiciansroutinely use to guide catheters or other invasive devices into adesired arterial branch or other location. In addition, the disclosedcatheter requires imaging through both the sheath and the balloonmaterials. As will be appreciated by those of skill in the art, thislimits image quality because it is difficult to entirely rid a balloonof air bubbles. Since the bubbles are strong acoustic reflectors, theydegrade image quality. Also, each layer of material between theultrasound transducer and the artery creates opportunities for signalattenuation, which decreases sensitivity, and for acousticreverberations, which introduce imaging artifacts. Finally, thedisclosed catheter is of a larger diameter than is necessary for imagingwith a given probe because the transducer is covered by both the sheathand the balloon, rather than just the sheath.

A catheter disclosed in U.S. Pat. No. 4,841,977--Griffith et al. shows atype of transducer array with a covering dilation balloon. The discloseddevice is not, however, well suited to imaging when the balloon isdeflated. In addition, the described system produces poor qualitytwo-dimensional ultrasound images because of the limited number ofdifferent ultrasound data lines available to form each image.

U.S. Pat. No. 4,917,097--Proudian, et. al. describes a dilation/imagingcatheter in which a large number of transducers, e.g., sixty-four, arearranged in an array and interfaced to special purpose integratedcircuits mounted beside the transducer array at the distal end of thecatheter. The balloon is slightly proximal of the array. The arrangementuses a steerable guidewire for catheter placement but exhibits a numberof significant limitations. For example, the ultrasound transducers,circuits, and signal processing hardware incorporated into the catheterare substantially more complex than the corresponding elements of amechanically scanned (rotating) system. In addition, the catheter slidesalong in contact with the artery (or other lumen) wall whenever theultrasound imaging plane is moved, thereby failing to minimize trauma.

Thus, it can be seen that there is a long recognized, yet unfulfilledneed for a catheter design which incorporates both a dilation balloonand an ultrasound imaging probe which, for reasons of simplicity andcost, is preferably mechanically rotated. Moreover, it would bedesirable to provide such a catheter that is manipulated into place witha steerable guidewire for ease and speed of use. It would also bedesirable to provide such a catheter design that minimizescross-sectional area so as to be useable in small lesions, arteries orlumens. It is therefore an object of this invention to provide acatheter apparatus for combined balloon dilation and ultrasonic imaging.Another object of the present invention is to provide a dilation/imagingcatheter of small cross-section in its distal length. A further objectof the invention is to provide a single lumen/dual lumen transition in acatheter that facilitates passing the guidewire from the single lumenand into a specified lumen of the dual lumen section of catheter.Another object of the present invention is to provide methods of usingcatheters. An additional object of the present invention is to provide amethod of backloading a guidewire from a single lumen section of acatheter and into a chosen lumen of a dual lumen section.

SUMMARY OF THE INVENTION

These and other objects are attained, for example, by one preferredembodiment of the present invention that provides a flexible catheterfor positioning a dilation balloon and an ultrasound transducer within aselected region of a patient lumen. The catheter comprises a distal tipsection with a tip lumen adapted to accept a guidewire, a single lumen,imaging-window section connecting proximally to the distal tip section,a dilation section connecting proximally to the imaging-window sectionand a triple lumen section extending proximally from the dilationsection.

The dilation section comprises a balloon with a length of flexibletubing (defining the balloon lumen) passing through the balloon, and asecond tube entering the proximal end of a balloon for inflation anddeflation. The distal end of the balloon sealingly attaches to thelength of tubing. The proximal end of the balloon sealingly attachesaround both the length of flexible tubing and second tube.

The triple lumen section comprises a guidewire lumen adapted to accept aguidewire, a probe lumen adapted to accept an ultrasound probe, and aninflate/deflate lumen, defined by the second tube, for operating thedilation balloon. The guidewire and probe lumens come together as asingle lumen in a transition proximal of the balloon and connect withthe balloon lumen.

The probe lumen, balloon lumen, and imaging section lumen are sized andconnected such that the tip of an ultrasound probe may be inserted intothe proximal end of the probe lumen, slide through the probe lumen,through the balloon lumen and into the lumen of the imaging windowsection.

The guidewire lumen, balloon lumen, imaging window lumen, and distal tiplumen are sized and connected such that a guidewire can be passedthrough them.

Most preferably, the catheter of the present invention includes atapered flexible distal tip which has a tip lumen for accepting aguidewire; the tip also preferably contains a radio opaque marker forX-ray viewing. Similarly, one or more radio opaque markers are placednear or within the balloon section for X-ray visualization.Additionally, in certain embodiments of the present invention, a "quad"lumen section comprising a fourth lumen is provided in place of thetriple lumen section.

The present invention also discloses methods of imaging and dilating apatient lumen by using apparatus substantially made in accordance withthe above-described invention, an ultrasound probe, and a guidewire. Theguidewire is advanced through the subject until the distal tip of thewire is distal to the region to be imaged and dilated; the catheter isthen advanced over the wire until the imaging window section has passedinto the region to be imaged. The wire is then withdrawn from the singlelumen portion of the catheter while holding the catheter stationary (inthe distal or proximal directions) within the subject and leaving thedistal tip of the wire within the guidewire lumen. The ultrasound probetip is next advanced into the imaging window section while holding thecatheter stationary within the patient lumen, and the probe is activatedto obtain ultrasound images. The probe tip is then retracted into theprobe lumen, the guidewire tip pushed distal of the catheter tip. Thecatheter is advanced over the wire (while the guidewire tip remainsdistal of catheter tip) until the balloon is within the region to bedilated. The balloon is inflated and/or deflated in accordance withstandard procedures. Next, the catheter is moved proximally so that theimaging window section is across the now dilated area and the wire tipis retracted into the wire lumen, wherein either the catheter or theguidewire is moved first. The probe is then advanced (moved distally)into the imaging window section and images obtained by activating theprobe. Finally, the catheter, probe and guidewire are withdrawn from thepatient.

The preceding described an image-before-dilate, dilate,image-after-dilate sequence. It is understood, however, that theinvention is not limited to this one sequence. For example, ifimage-after-dilate revealed the need, one could perform a seconddilation by simply repeating the required steps. In addition, it willsometimes be desirable to omit portions of the sequence. For example,imaging may show that dilation is unnecessary and hence the dilation isomitted. For these reasons, the descriptions of the invention set forthherein are not to be construed as limiting the invention, and referenceshould be made to the claims to determine the true scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willappear after careful consideration of the preceding and followingdescriptions, including reference to the drawings in which:

FIG. 1 is a longitudinal cross-section of the distal end of a cathetermade in accordance with the present invention.

FIG. 1A is a longitudinal cross section, similar to FIG. 1, of a sectionof a catheter having a fourth lumen.

FIG. 2 is a cross-sectional view of a catheter made in accordance withthe present invention, taken along line 2--2 in FIG. 1.

FIG. 3 is a cross-sectional view of a catheter made in accordance withthe present invention, taken along line 3--3 in FIG. 1.

FIG. 4 is a cross-sectional view of a catheter made in accordance withthe present invention, taken along line 4--4 in FIG. 1.

FIG. 5 is a cross-sectional view of a catheter made in accordance withthe present invention, taken along line 5--5 in FIG. 1.

FIG. 6 is a cross-sectional view of a catheter made in accordance withthe present invention that is being back loaded in accordance withcertain aspects of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a distal portion of a catheter 100 made inaccordance with the present invention is illustrated. Those of ordinaryskill will understand that catheter 100 is substantially tubular andflexible, and that FIG. 1 shows a longitudinal cross-section of thecatheter. Those of ordinary skill will also be familiar with the typesof materials and methods used to build such catheters. Preferably, thecatheter 100 of the present invention is lubricated on its exteriorsurface and the interior lumen surfaces may also be coated withlubrication. Assuming a coronary artery application, the completecatheter is preferably about 1.0 to 1.5 meters long. The distal tip 101of the catheter 100 is preferably about 1.0 cm long and flexible so thatit may be advanced over a guidewire (not shown) that has been threadedthrough a coronary artery or other patient lumen. The distal tip 101 ofcatheter 100 is also preferably soft and tapered so that it isatraumatic to the artery or lumen wall. The inside diameter of thedistal tip 101 is preferably also tapered as shown in FIG. 1; this taperpermits a guidewire to smoothly move distally through the distal tip101, which is preferably radio opaque or contains an opaque marker 110,as shown, to indicate the catheter tip location in X-ray views. Thetapered inside diameter of the distal tip 101 is preferably sized toslidingly accept a guidewire and is most preferably between about 10 to20 mils (0.010-0.020 inches) in diameter for coronary imagingapplications.

The imaging window section 106 of the catheter 100 connects proximallywith the distal tip 101 and is a flexible, elongated, substantiallytubular section that is also substantially transparent to the acousticenergy used for imaging. The diameter of the lumen of the imaging windowsection 106 is sized to pass either a guidewire or an ultrasound imagingprobe. The outside diameter of the imaging window section 106 is mostpreferably a few thousandths of an inch larger than the inside diameter.A wide range of choices exist for selecting the length of this portionof catheter 100. A relatively long imaging window section 106 having alength of about 10 cm (3.9 inches), allows collecting images over a longlength of the patient lumen in which the catheter 100 is placed bymoving the probe longitudinally without repositioning the catheter 100.For example, a relatively long imaging window section 106 is useful forsearching for a suspected stenosis or in three-dimensional imaging. Onthe other hand, a relatively short imaging window section 106, of about2.0 cm (0.8 inches), allows a dilation with much less catheterpositioned distal of the stenosis. Thus, for example, in a percutaneoustransluminal coronary angioplasty (PTCA) procedure a short window may beappropriate because of limited space in the artery past the stenosis.The important point is that length of the imaging window section 106 isbased upon the intended application.

The dilation section 107 of the catheter 100 of the present inventionconnects proximally with the imaging window section 106. It includes aballoon 104 that can be inflated or deflated by passing a fluid througha tube 105. The tube 105 is adjacent a length of flexible tube 109 whichforms a passage for passing a guidewire or an ultrasound probe throughthe balloon 104. The distal and proximal ends of the balloon 104 connectsealingly with the tubes 105,109. The spaces shown in FIG. 1 between theballoon 104 and the tubes 105,109 are for clarity of presentation. Aswell known to those of skill in the art, balloon sizes are applicationdependent as with known dilation catheters. Radio opaque markers 102,103are also included so that the location of the dilation section 107 canbe determined. However, variations are possible; for example, in certainembodiments, the radio opaque markers 102,103 are placed just proximaland distal of the balloon 104 to delineate its length. In anotheralternate embodiment, the radio opaque markers 102,103 are replaced witha single marker (not shown) that locates the center of the balloon orsome other known point within the dilation section 107.

The cross-sectional arrows 2--2 shown in FIG. 1 indicate a locationwithin the triple lumen section 111 of catheter 100. FIG. 2 illustratesthis cross-section. The triple lumen section 111 is a tubular flexibleelongate member containing at least three lumens 120,121,122.Preferably, a probe lumen 120 is sized to slidingly accept an ultrasoundprobe, a wire lumen 121 is sized to slidingly accept a guidewire, and aninflate/deflate lumen 122 is provided; the size of the latter affectsthe time required to inflate and deflate the balloon 104. However, asshown in FIG. 1A, a fourth lumen 220 is also provided in certainembodiments.

Referring still to FIG. 2, it should be emphasized that, in the regionnear arrows 2--2, FIG. 1 depicts a cross-sectional view of the catheter100 taken along the irregular line A--A. This cross-section has beenchosen in order to clarify the function of various lumens. Similarly,the cross-section of FIG. 1 shown near arrows 3--3 is depicted in FIG.3, and this cross-section is obtained by sectioning as indicated byarrows B--B in FIG. 3. Finally, the cross-section of FIG. 1, shown neararrows 4--4, is obtained by sectioning as indicated by arrows C--C inFIG. 4.

Referring again to FIGS. 1-2, the length of the triple lumen section 111of catheter 100 is application dependent; it extends proximally tonearly the proximal end of the catheter 100 (not illustrated) whereappropriate fittings, adapters, connectors, valves and seals, all wellknown within the art, are added. In a catheter intended for PTCA, thetriple lumen section 111 is preferably between about 100 cm (39.4inches) to 150 cm (59.1 inches) in length. The probe lumen 120 andinflate/deflate lumen 122 extend essentially the complete length of thetriple lumen section 111; the guidewire lumen 121 extends the completelength in certain preferred embodiments. In other preferred embodiments,the guidewire lumen 121 extends proximally from about the location ofarrow 3--3 shown in FIG. 1 for a fraction of the triple lumen length.For instance, a 20-30 cm (7.9-11.8 inch) guidewire lumen 121 can be usedfor PTCA catheters. As used herein, the term "triple lumen length"refers to the longest of the three lumens, 120,121,122. For example, ifthe guidewire lumen 121 is 25 cm (9.8 inches) long and the probe lumen120 and inflate/deflate lumen 122 are 120 cm (47.2 inches) long, thenthe catheter has a 120 cm (47.2 inch) long "triple lumen length."

Referring still to FIGS. 1-3, another embodiment of the guidewire lumen121 extends the full length of the triple lumen section 111 except for ashort interruption where the exterior wall is removed to expose thelumen 121. This embodiment allows a single catheter to be used as if theguidewire lumen 121 ran the full length of the triple lumen section 111or as if the guidewire lumen 121 extends proximally from arrows 3--3 inFIG. 1 for a fraction of the triple lumen length.

A "transition" region in the vicinity of line 3--3 of FIG. 1 joins theguidewire lumen 121 and probe lumen 120 into a single merging lumen 125which then extends distally through the balloon 104 and imaging windowsection 106. The merging lumen 125 of the transition region is mostpreferably constructed in accordance with invention disclosed in U.S.patent application Ser. No. 773,037 filed on Oct. 8, 1991 entitled"Ultrasonic Imaging Sheath" naming James M. Griffith as the inventor,the entirety of which is incorporated by reference as if fully set forthherein. As disclosed therein, a catheter is constructed with a distallumen that terminates with a distal tip having a tip lumen sized toaccept a guidewire. The distal lumen is connected to a dual lumen regionhaving a probe lumen and a wire lumen by an intermediate section thatadvantageously permits the alternate acceptance of either the guidewireor the probe in the intermediate lumen. The construction details,methods of use and other advantages of the disclosed invention may befound in the referenced specification, which is incorporated herein inits entirety by reference thereto.

Thus, as shown in FIG. 1 the probe lumen 120 is directly connected tothe merging lumen 125 and passes through the balloon 104, while theguidewire lumen 121 is offset. However, it will be understood that thisis just one example of how the transition region can be offset from thelumen passing through the balloon 140. The transition region is smoothlytapered on its outside surface to make catheter 100 atraumatic to thepatient lumen being imaged.

Another aspect of the present invention is that the transition regioncontains a design feature which makes "back loading" a guidewire into acatheter very easy. As known in the art, back loading refers to thepractice of threading the proximal end of a wire into the distal end ofa catheter lumen and then moving the end of the wire through the wirelumen until it exits the proximal end of the catheter lumen. Thecatheter 100 of the present invention is easily "back loadable" but, asthe wire goes through the transition region it might enter the probelumen 120 rather than the guidewire lumen 121 unless some structure orprocedure prevents this mistake. As shown in FIGS. 3 and 5, the presentinvention provides a design feature which simplifies such back loadinginto the guidewire lumen 121. The larger transition lumen 125 shown inFIG. 3 illustrates the guidewire lumen 121 and probe lumen 120 joiningtogether in the transition lumen 125, as described above. Thistransition lumen 125 consists of large radius and small radius arcsjoined by approximately straight lines, angled like the sides of afunnel; the larger arc portion aligns with a probe lumen wall, while thesmaller arc aligns with a guidewire lumen wall. FIG. 5 illustrates across section of catheter 100 taken at arrows 5--5 in FIG. 1; thecross-section is taken at a location distal of where the wire lumen 121and probe lumen 120 join. FIG. 5 shows the ridge 130 of catheter bodymaterial between the lumens 120,121, and also shows how the transitionregion lumen 125 aligns with the probe lumen 120 and wire lumen 121. Thecircumferential position of the guidewire lumen 121 is preferablyvisibly marked on catheter 100; the mark can be provided, for example,with a colored stripe (not shown) in the triple lumen region 111 or bythe position and shape of a radio opaque marker 129.

Thus, in order to back load a guidewire into catheter 100 of the presentinvention: (1) insert the wire into the distal catheter tip, (2) bendthe catheter so that the transition region resembles an arc with theguidewire lumen away from the center of curvature; and (3) push the wireproximally into the wire lumen 121. Since, in the absence of deflectingforces, the guidewire is basically straight, bending the catheter 100causes the tip of the wire to drop into the narrow end of theabove-described "funnel." The narrow end of the funnel aligns with theguidewire lumen 121 and hence, the guidewire passes into the guidewirelumen 121 when the wire moves proximally within the catheter 100. Thefunnel (and hence the transition region) preferably has a longitudinallength of about 1 cm (0.4 inches) so that a gentle curvature providesreliable back loading.

The preceding description of the transition region 125 is for the casewhere the probe lumen 120 is of larger diameter than the guidewire lumen121. The description is modified if the probe lumen 120 and theguidewire lumen 121 are of equal diameter, or if the guidewire lumen 121is larger than the probe lumen 120.

The position of the transition region 125 and hence the distal end ofthe wire lumen 121 and probe lumen 120, is designated or inferred inX-ray views from one or more radio opaque markers 129 placed as shown,in or near the transition region 125.

In the preceding description of back loading those of skill in the artwill appreciate and understand that the guidewire and catheter movementsare relative; a proximal guidewire movement is equivalent to a distalcatheter movement.

It is also known in the art that changing catheters while leaving theguidewire in place using conventional "over-the-wire" PTCA catheters isdifficult. A solution to this problem is the so-called "rapid exchange"catheter, wherein the guidewire lumen runs only for a fixed distancealong the distal end of the catheter, e.g., a distal section about 0.8feet (25 centimeters) long. Although these designs eliminate the needfor crimping additional lengths of guidewire to the proximal end, thecatheter may not "track" the guidewire as well as desired. A furtherimprovement to the "rapid exchange catheter" is the so-called"convertible" catheter that includes an opening in the sidewall of aguidewire lumen; the opening permits the guidewire to be passed ineither over-the-wire or rapid exchange fashion. The present inventionmay be adapted for use as either a "rapid exchange" catheter byshortening the proximal end of the guidewire lumen, or, alternatively,an opening can be provided in the sidewall to permit the catheter of thepresent invention to function as a "convertible" catheter.

The present invention also provides improved methods of performingballoon dilation and intraluminal ultrasonic imaging within a subject.For example, the catheter 100 of the present invention described abovecan be used for a PTCA procedure. An ultrasound probe is inserted intothe probe lumen 120 with the distal tip of the probe proximal to thetransition region 125. Doses of contrast media are supplied where neededto allow X-ray visualization and anatomic orientation. A guidewire isintroduced through a guiding catheter and into the proper coronaryartery. After the wire tip is positioned on the distal side of therestriction or lesion, the wire is used to guide the catheter 100 of thepresent invention into the coronary artery. The imaging window section106 is placed across the stenosis using X-ray visualization, and thewire is retracted so that the distal tip of the wire resides in the wirelumen 121 and is proximal of the transition region 125. An ultrasoundimaging probe is then advanced into the imaging window section 106 toobtain pre-dilation ultrasound images. Next, the probe is retracted intothe probe lumen 120, the guidewire advanced distal of the catheter 100,and the catheter 100 is moved distally so that the balloon 104 crossesthe lesion, and the balloon 104 is then inflated to dilate the lesion.After the balloon 104 is deflated, the catheter 100 is moved proximallyuntil the imaging window section 106 is again across the lesion.Portions of the procedure are then repeated as necessary to obtainpost-dilation ultrasound images. Although an "image/dilate/image"sequence is described above, it will be understood that other sequencesare also useful. For instance, if post-dilation imaging revealed theneed, a second dilation could be performed. Use of the present inventionhas been described in a PTCA application. It is understood, however,that the catheter 100 disclosed herein can also be used in otherinvasive procedures involving various body lumens.

Additionally, those of skill in the art will realize that a fourth lumen220 could be incorporated proximal of the dilating section in thecatheter 200 as illustrated in FIG. 1A and described above. As shown,the fourth lumen joins the lumen 120 and the lumen 121 in the vicinityof the cavity 105, it being understood that like reference numeralsrefer to the structure shown in and described with reference to FIG. 1.The location where the lumens 220,120,121 merge could be movedproximally. Alternatively, the fourth lumen 220 can be connected to theballoon lumen at a point distal of the connection point shown in FIG.1A. The catheter 200 could then be used to deliver other devices, probesor sensors and the like, permitting other signals or substances to beintroduced into the patient, other parameters monitored or othertherapies initiated. Furthermore, those of ordinary skill will realizethat the probe lumen 120 in the catheter 100 shown in FIG. 1 need notnecessarily contain an ultrasound probe. The probe lumen 120 could beused to deliver other devices, probes or sensors and the like,permitting other signals or substances to be introduced into thepatient, other parameters monitored or other therapies initiated.

In addition, those of ordinary skill will realized that while FIG. 1shows the preferred location on the catheter to seal the proximal end ofthe balloon, other locations such as on the distal end of the triplelumen section can also be used.

Although the present invention has been described in what is presentlyconsidered the most practical and preferred embodiment it is to beunderstood that the invention is not to be limited to the disclosedembodiment. The invention is intended to cover the various modificationsand equivalent arrangements included within the spirit and scope of theappended claims.

What is claimed is:
 1. A method for sequentially imaging and dilating aregion of a subject:using an ultrasound probe, a guidewire, and acatheter, wherein the catheter comprises an elongate, flexible memberhaving a lumen in its distal length; a dilation balloon attached to aproximal portion of the distal length, the outside of the distal lengthand the balloon being sized for passage into the region of the subjectand the lumen having a diameter sized to accept either the guidewire orthe ultrasound probe, wherein the lumen splits into a dual lumenproximal of said balloon, the dual lumen comprising a guidewire lumensized to accept the guidewire and a probe lumen sized to accept theultrasound probe, the flexible member further comprising a third lumenwherein the third lumen communicates with the balloon, the methodcomprising the steps of: advancing the guidewire through the subjectuntil a distal tip of the guidewire is distal of the region of thesubject to be imaged; advancing the catheter along the guidewire untilthe distal portion has passed into the region to be imaged; pulling theguidewire proximally while holding the catheter relatively stationary inthe distal and proximal directions within the subject, and leaving thedistal tip of the guidewire within the wire lumen; advancing theultrasound probe tip into the distal lumen portion of the catheter;preventing the ultrasound probe from extending distally beyond thecatheter; activating the probe to obtain pre-dilation ultrasound imagesof the region; retracting the probe into the probe lumen; advancing theguidewire distally of the catheter tip; moving the catheter distallyuntil the balloon passes into said region of the subject; and inflatingand then deflating the balloon.
 2. The method of claim 1 furthercomprising post-dilation imaging steps of:repeating the steps forreplacing the guidewire with the probe in the distal length of catheterand obtaining post-dilation ultrasound images.
 3. The method of claim 1,wherein the step of imaging is performed by transmitting ultrasoundsignals through the balloon.
 4. A method for sequentially dilating andthen imaging a region of a subject:using an ultrasound probe, aguidewire, and a catheter, wherein the catheter comprises an elongate,flexible member having a lumen in its distal length; a dilation balloonattached to a proximal portion of the distal length, the outside of thedistal length and balloon being sized for passage into the region of thesubject and the lumen having a diameter sized to accept either theguidewire or the ultrasound probe, wherein the lumen splits into a duallumen proximal of said balloon, the dual lumen comprising a guidewirelumen sized to accept the guidewire and a probe lumen sized to acceptthe ultrasound probe, the flexible member further comprising a thirdlumen wherein the third lumen communicates with the balloon, the methodcomprising the steps of: advancing the guidewire through the subjectuntil a distal tip of the guidewire is distal of the region of thesubject to be imaged; advancing the catheter through the distal lumenand the guidewire lumen, until the balloon has passed into the region tobe dilated; inflating and then deflating the balloon by flowing a fluidthrough the third lumen; pulling the guidewire proximally, and leavingthe distal tip of the guidewire within the wire lumen; advancing theultrasound probe tip into the distal lumen portion of the catheter;preventing the ultrasound probe from extending distally beyond thecatheter; and activating the probe to obtain post-dilation ultrasoundimages of the region.
 5. The method of claim 4 further comprising thesteps of:moving the catheter proximally prior to imaging so that theballoon is located proximal to the region of the subject.
 6. A catheterfor ultrasound imaging and balloon dilation within a region of apatient, comprising:a flexible distal tip portion with a tip lumenhaving a diameter greater than a guidewire diameter and less than aprobe diameter; a flexible imaging window section having a lumenconnected to the tip lumen, and having a diameter larger than saidguidewire or said ultrasound probe, and being connected to a proximalend of the lumen; a flexible balloon dilation section comprising: aballoon with an inflate/deflate tube; and a through tube, wherein athrough tube lumen in said through tube alternately accepts theguidewire or the probe; the through tube lumen connected proximally withthe lumen in the imaging window section; a flexible lumen portioncomprising: an ultrasound probe lumen, a guidewire lumen, and aninflation/deflation lumen; and a flexible transition region between theflexible lumen portion and the balloon dilation section, wherein theprobe lumen and the wire lumen join into a single lumen that connectsproximally to the through tube.
 7. The catheter of claim 6 wherein thedistal tip portion comprises a tapered section and a radio opaque markerfor X-ray viewing.
 8. The catheter of claim 6 wherein the flexible lumenregion further comprises a fourth lumen.
 9. The catheter of claim 6wherein the probe lumen and the dilation section through-tube lumen arecoaxial.
 10. The catheter of claim 6 wherein the wire lumen connectswith the through tube lumen at a longitudinally tapered transition. 11.The catheter of claim 10 wherein the longitudinally tapered transitioncomprises, in cross section: a first arc, a second arc, and a pair ofsubstantially straight sidewalls connecting the first arc and the secondarc.
 12. The catheter of claim 6 wherein the guidewire lumen extendsproximally for only a portion of the length of the probe lumen and theinflate/deflate lumen.
 13. A method of imaging and dilating a region ofa lumen in a subject comprising the steps of:positioning a guidewire sothat the distal tip of the guidewire is within the lumen and distal of aregion of the lumen to be imaged and dilated; advancing a catheter usingthe guidewire as a guidance device until a distal end of the catheter iswithin the lumen, and distal of the region of the lumen to be imaged anddilated; retracting the guidewire until it becomes proximal of theregion of the lumen to be imaged and dilated; advancing an ultrasoundprobe within the catheter until the tip is within the region of thelumen to be imaged and dilated; preventing the ultrasound probe fromextending distally beyond the catheter; activating the probe to obtainimages; advancing the catheter using a method comprising the steps of:retracting the probe, advancing the guidewire, and moving the catheterdistally using the guidewire as a guidance device until a baloondilation portion of the catheter is within the region to be imaged anddilated; and dilating the region of the lumen in the subject bytemporarily inflating the balloon through a catheter lumen.
 14. Themethod of claim 13 wherein the imaging is performed through the balloonand the steps of moving the catheter between imaging and dilation areomitted.
 15. A catheter with a transition region for back loading aguidewire through a single lumen and into a selected lumen of a multiplelumen section where the single lumen divides into two or more lumens,comprising:a transition region containing a cavity through which thesingle lumen connects with at least one of the multiple lumens, theshape of the cavity in a cross-section perpendicular to a longitudinalaxis of the catheter, the section taken where the lumens connect, beingdefined by: a first arc and a second arc connected by two substantiallystraight side walls,wherein the cavity cross-section gradually blendsinto the single-lumen cross-section over a longitudinal distance of atleast about two lumen diameters.
 16. The catheter of claim 15 furthercomprising a visual marker for revealing the circumferential position ofthe selected lumen within the elongate catheter.
 17. A method forbackloading a catheter comprising:a transition region for back loading aguidewire through a single lumen and into a selected lumen of a multiplelumen section where the single lumen divides into two or more lumens,the transition region containing a cavity connected to one or more ofthe lumens, the shape of the cavity in a cross-section perpendicular toa longitudinal axis of the catheter taken at a point where the lumensconnect, being defined by: a first arc and a second arc connected by twosubstantially straight side walls,wherein the cavity cross-sectiongradually blends into the single-lumen cross-section over a longitudinaldistance of at least about two lumen diameters; the method comprisingthe steps of: inserting the proximal end of the guidewire into thesingle lumen; bending the catheter so that a selected lumen of the twoor more lumens is on the outer surface away from the center ofcurvature; and moving the guidewire longitudinally into the selectedlumen.
 18. The method of claim 17 wherein the step of inserting theproximal end of the guidewire comprises inserting the guidewire into alumen that has a length beginning at the proximal end and running lessthan full length.
 19. The method of claim 17 wherein the step ofinserting the proximal end of the guidewire comprises inserting theguidewire the transition region, into said selected lumen, moving theguidewire proximally, and passing the proximal end of the guidewireoutside the catheter through an opening in the wall of the selectedlumen.
 20. The catheter of claim 6 wherein the guidewire lumen extendsthe length of the probe lumen; and further comprising an openingconnecting the guidewire lumen with a space outside the catheter, saidopening disposed between the distal and proximal ends of the guidewirelumen.